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Sr15

(Watson and Luig, 1966) (Plate 3-18)

Sr15 is completely associated with genes Lr20 and Pm1 (Watson and Luig, 1966; McIntosh, 1977), hence the genetics of these factors are relevent to those for Sr15. On the basis of mutation studies, McIntosh (1977) concluded that Sr15 and Lr20 were the same gene.

Chromosome Location

7A (Sears, 1954); 7AL (Sears and Briggle, 1969). Distally located to Sr22 (The and McIntosh, 1975).

Origin

Common wheat. Although Sr15 was first described in cv. Norka, it was known to be present in some unrelated cultivars.

Pathogenic Variability

Pathogenic polymorphisms occur for Sr15 in most geographical areas. However, virulence levels tend to be very high except in Australia, parts of Africa and North America (Luig, 1983; Huerta-Espino, 1992). Pathotypes can be grouped according to the infection types produced on selected genotypes under controlled conditions. At least five levels of pathogen responses can be distinguished among the Australian pathotype collection (Luig, 1983). Pathotypes giving the higher intermediate responses would be classified as virulent in many laboratories, or if temperatures exceeded 18-20°C.

Reference Stocks

Source Stocks

All wheats with Lr20 and Pm1. However, some mutants lacking Pm1 but possessing Lr20 and Sr15 were generated in the mutagenesis study of McIntosh (1977).

Africa: Kenya W744 Sr9b.

Australia: Angas; Aroona; Fedka. Festival Sr9b. Tatiara Sr9b Sr12.

Europe: Anfield; As II; Maris Halberd; Sappo; Timmo.

USA: Wared.

Seedling leaves of (L to R): Norka, Thew, CS*5/Axminster 7A, 77.5056, 77.5058 and Chinese Spring; infected with pt. 343-1, 2, 3, 5, 6 [P15] at A. 18°C and B. 23/28°C. Set C. is infected with pt. 194-2 [P15] and D. with pt. 21-1, 2, 3, 7 [p15] and incubated at 20°C. Comparisons of the first three genotypes show the effects of genetic background on infection type. Lines 77.5056 and 77.5058 are non-mutant and mutant lines, respectively, extracted from a mutation experiment aimed at the Sr15/Lr20 gene. In addition to the small difference in incubation temperature, pt. 194-2 is less avirulent than 343-1, 2, 3, 5, 6 under comparable conditions. Pt. 21-1, 2, 3, 7 is fully virulent at all temperatures on seedlings with Sr15. Lines 77.5056 and 77.5058 display a lower IT indicating a second gene in A., B. and C.

Use in Agriculture

Sr15 gives satisfactory protection to avirulent pathotypes at lower temperatures. However, the high degree of pathogenic variation and temperature sensitivity make it extremely unreliable. At best, it has been used as a fortuitous component of oligogenic resistances.

Breeder's Toolbox

Ug99 Effectiveness:

-Virulence for the gene is known to occur in other races-Level of resistance conferred in the field usually inadequate under high disease pressure-Data from multiple research groups are not consistent; initial studies determined Sr15 was ineffective however recent data shows avirulence in Ug99 lineageSource:RustTracker.org